assign shutdown command to sleep button fails 17.10 and 18.04

Hi,
I'm running a GigaByte Brix with a wireless Logitech K400 Keyboard. The said keyboard features a "power off" button that is interpreted by Ubuntu as "Sleep" for some reason. On the 17.04 release it was possible to simply assign the shutdown command to this button and everything was fine.
With 17.10 and 18.04 LTS (beta) the behaviour of this button can not be changed. If I try to assign my shutdown command and press the button, my system immediately enters suspend mode. Even if I try to simply read out the key code of the button it will directly go to suspend.
Will there be a way of getting back the behaviour of 17.04 so that I can freely choose what this button does?